Extractive distillation of oxygenated organic compounds



All@ 19, 1952 T. Q. ELIO-r ETAL ExTRAcTIvE: DISTILLATION oF oxYGr-:NATED 'ORGANIC coMPouNns Filed April 15. 1949 cuFroN s.c1ooonN,JR. 'JosePl-s c. wEAvER JR.

` INVENTOR'.

ATTORN EY Patented Aug. 19, 1952 oFFicE EXTRACTIVE DISTILLATION' 'or'v OXYGEN- ATED ORGANIC COMPOUNDSl Theodore Q. Eliot, Clifton S.v Goddin, Jr., and Joseph C. Weaver, Jr., Tulsa, Okla., assignors to Stanolind Oil and Gas Company, Tulsa, Okla., a. corporation of Delaware Application April 15, 1949, Serial No. 87,698

7 Claims. (Cl. Zim-39.5)

Our invention relates to a method for separating certain organic compounds from one another and from complex organic mixtures in which at least some of the components thereof form azeotropes with one or more of the constituents present therein. More particularly, it relates to the separation of ethanol, isopropanol, and methyl ethyl ketone from one another and from complex aqueous mixtures containing these and other organic compounds.

Mixtures of the type contemplated by our invention are encountered in the water soluble chemicals fraction obtained in the now generally known hydrocarbon 'synthesis process involving the reduction of carbon monoxide with hydrogen in the presence of a fluidized iron catalyst. In vthe hydrocarbon synthesis plants now designed for commercial purposes, having capacities of the order oi 6000 barrels of liquid hydrocarbons per day, the chemicals present in mixtures vof the type contemplated by the process of our invention constitute approximately 30 per cent of the total Water soluble chemicals produced or about 140,000 lbs. per day. Accordingly, for economic and other reasons, it is essential that these chemicals be recovered, each in as highlyy puriiied form as possible.

Mixtures typical 'of those with which We are concerned and the relative concentrations in Some appreciation of the diculties encountered in attempting to obtain any or all of the abovementioned oXygena-ted `organic compounds in a vsubstantially pure form when present in such mixtures may be realized by reference to the boiling points :ofthe .pure .con'i1c101.1nt`xs, :as -Well as 4to their azeotropes either 4in the'faqueous '0r 'anhydrous state'. v

Boiling points of pure chemicals B. P.' C. Butyraldehyde 75.7 Ethyl acetate 77.1 Ethanol 7.8.4 Methyl ethyl ketone v79.6 Isopropanol 82.4 Methyl propyl ketone V102.0

Boiling points of aeeotropes p o B-Rg-C. Butyraldehyde-ethanol-Water 67.2 Butyraldehyde-water `68.0 Ethanol-ethyl acetate-WatchA 70.3 Ethyl acetate-water 70.4 Ethyl acetate-ethanol V'71.8 Ethanol-methyl ethyl ketone-water 73.2 Methyl ethyl ketone-water "73.5 Ethanol-methyl ethyl ketone 74.8 Ethyl acetate-methyl ethyl ketone; 76,7 Ethanol-methyl propyl ketone: A 77:7 Ethanol-methyl propyl .ketone-water 718.1 Ethanol-Water 7.8.:2 Isopropanol-WaterA '80A Methyl propyl ketone-Water Y33.9

It'will be readily apparent to one skilled in the art to which our invention relates, that the separation in substantially pure form of even a single component from aqueous mixtures of lthe -above type presents a formidable recovery problem. Even if Water were removed from this mixture 'by one of several methods, fractionation of the anhydrous chemicals to yield pure products would not be practicable. f

It is an object of our invention to provide an efficient method for the 'separation of ethanol, isopropanol, methyl A ethyl ketone, and methyl propyl ketone from complex mixtures of the `type referred to above. It is a further object of our invention to provide a process for obtaining highly puried ethanol from mixtures of the aforesaid type,which meets A. C. S. purty're.- quirements with respect-to isopropanol, i. e., not more than 30 parts of isopropanol per million parts of ethanol.;

We have now discovered that the foregoingand other objects can `be accomplished by subjecting crude mixtures of the type described .abovetp'a .series of Aextractiva distillations with water. Ac-

4isopropanol and traces of other impurities.

`cording to the process of our invention, a crude mixture of the aforesaid type is extractively distilled with water, whereby the bulk of the ethanol is washed down the column in the form of a dilute aqueous solution. In this step the fractionatingV tower is. operated under conditions such that an aqueous overhead fraction is secured which contains butyraldehyde, ethyl acetate, methyl ethyl ketone, methyl propyl ketone, isopropanol, and some ethanol. The most dicult component to separate from the ethanol is isopropanol, and we that the concentration of .water in the liquid within the column is'from about 90 to 99 mol per cent, preferably in the range of 95 m01 perA cent. The amount of net distillate drawoff is carefully controlled so that ethanol of the desired purity is produced. The amount of heat supplied to the column is normally in the range of 100 to 150 B. t. u./lb. of bottoms. A minimum amount of heat is required to secure satisfactory stripping of The use ofV excessive amounts of heat beyond the strip- `ping requirement impairs the eiciency of the vcolumn due primarily to decreasing water concentration nwithin the column. The temperatures vemployed may vary widely, but for the majority of'feeds We have found that the tower bottom temperatures range from about 90-98 C., preferably about 96 C., (corrected to atmospheric pressure) and the overheadrtemperatures range from about r13438 C., preferably about 76 C.

4found to be in the neighborhood of 60 to 80 per -cent of the 'total chemicals'present, while isopropanol is generally present in a concentration of from about 1 to 3 per cent.y Accordingly, we have found that with mixtures ofthe aforesaid type a satisfactory separation of the isopropanol from the bulk ofthe ethanol may be effected by taking overhead in the initial distillation step a quantity of ethanol corresponding to from I, about 1 to about 10'weight; per cent of that in the originalfeed mixture. Thus, for example, with a fractionating column having 65 plates and operating at an eiiciency of 50 to 60 per cent, We have observed that by taking Y.overhead only about 1.3 weight per cent of the ethanol originally present in the feed, a highly purified form of .ethanol (containing about parts per million of isopropanol) can be obtained. With more efficient fractionating columns the amount of ethanol required to be taken overhead becomes less than 1 weight per cent. However, as the 'concentrationvof ethanol in the feed decreases ortherelative percentage of isopropanol in the vfeed increases (with a given column and other operating conditionsremaining constant), it becomes necessary to withdraw higher percentages 'fof ethanol in the overhead in order to insure aV isopropanol from the ethanol in the bottoms. For

substantially complete separation of the example, with feeds in which the ratio of ethanol to isopropanol is of the order of l0 to 1 instead of about 30 to 1, as is generally the proportion in the case of hydrocarbon synthesis water-souble- Y chemicals mixtures, the amount of ethanol Withdrawn in the overhead may correspond to as much as about 20 weight per cent of that present in the original feed in order that a satisfactory removal of isopropanol may be achieved. The dilute aqueous ethanol solution from the base of the column is sent to a conventional fractionating column wherein a constant boiling mixture of ethanol and water of high purity is removed as distillate. The bottoms, which is essentially water, is recycled to provide dilution water for the extractive distillation operation described above. A portion of this water is continuously rejected to the sewer to provide a purge for any heavy impurities in the system.

The crude distillate from the above extractive distillation operation is then subjected to a second extractive distillation with water whereby methyl ethyl ketone, methyl: propyl ketone, ethanol, and isopropanol are washed down the column and an aqueous mixture of butyraldehyde and ethyl acetate is taken overhead as distillate. p

In general, it may be said that in order to effect a satisfactory separation of butyraldehyde and ethyl acetate from methyl ethyl ketone, methyl propyl ketone, ethanol, and isopropanol at this point, the dilution water should be added `to the column in an amount such that the concentration of Water in the liquid atany point in the column is from about 90 to 99 mol per cent and preferably about 95 mol per cent. The amount of net overhead withdrawn should be ycarefully controlled to avoid forcing methyl ethyl ketone, ethanol, or isopropanol overhead or butyraldehyde and ethyl acetate into the bottoms at this stage. Ordinarily the heat input should be in the range of -120 B.t.u./lb. of bottoms,

y preferably about 90 B.t.u./lb. of bottoms. It has been our observation, however, that the use of an excessive amount of heat impairs the eddciency of the column since under such conditions the concentration of Water in the column falls below the value we have found suitable for effecting the desired separation. In this connection, the temperatures employed mayy vary rather widely. For the majority of feeds, however, We have'found that bottom tower temperatures of from 82 to about 94 C. (corrected to atmospheric pressure), preferably about 85 C. and top'tower temperatures of from about 68 to about 77 C., preferably 71 C., are satisfactory. The overhead stream obtained in this operation is an aqueous mixture of butyraldehyde and ethyl acetate which may, if desired, be further separated into its individual components. The bottoms portion obtained as a result ofr this distillation step contains ethanol, isopropanol, methyl ethyl ketone, and methyl propyl ketone in a total concentration of the order of 1Y mol per cent. The dilute bottoms fraction contain ing these chemicals is introduced at an intermediate point in another fractionating column wherev a third extractive distillation operation is effected. In this separation step, however, the water azeotropes of methyl ethyl ketone and Vmethyl propyl ketone free of alcohols are collected as an overhead stream, a vdilute (from about 2 to 10 weight per cent) aqueous solution of isopropanol and ethanol is Withdrawn Afrom the column as a side stream below the point at whioh'th'e feed-isintroduced, `.while water is with drawn from the bottom of the column and-free cycled;V Iny effecting this separation dilution water is introduced at the topof the-'column indan amount such' that the *concentration of Water in the liquid :at any vpoint inthe-column 'above the point of side 'stream'withdrawalranges between about SOan-d 99 mol per cent, preferably y85 mol ,per cent. Heat input to the column will normally be between 125-300 B.t.'u^./lb. of bot toms. Under these conditions isopropanol and ethanolY relatively free from-ketones can be withdrawn in ther formV of an' aqueous 'solutionrasa side stream below the "point at whichthe feed is introduced. The observations relative'to heatinput discussed above are equallygpertinent. to .the separation of methyl ethyl ketone, methyl propyl ketone, and water from 'isopropanoL ethanol, and water.. While `the actual temperatures employed "at `this stage of our process may` varyY widely, we .have-'found that .in the majority of .instances the bottom temperature will be the boiling 'point ofwaten while top temperatures 'may be inthe ranger'of vfrom about '73 to y83 C, andfpreferably 'about' 74 C. The temperature at which the side stream 'of aqueous .isopropanoli andlethanol is withdrawn should generally range between 'about' 92 and about 99 C. '(oorlrectedto' 'atmosphe'rio .presure-l 'depending 'onv the lconcentrationselected for the drawoff stream..

.If desired, the methyl ethyl ketone-"and methyl propyl. ketone v'contained in: the distillate. .from this operation can be separated :by 'nrst removing the faze'o'tropic 4imiter andv then, separating the anhydrous ketones by '.rneanstjcn.` conventional fractional distillation. f

'TheV dilute aqueous side stream of :isopropanol and'ethanol is next introduced `atan intermedi- 'ate 'point of still another extractiva distillation column where isopropanol .is taken. ol'f `overhead and: ethanol is withdrawn 'as Aa bottoms'str'e'am. The lisoprop'anol 'is removed in the form offen -azeotrope 'with `water .by introducing the' vdilution water at fa point substantially below the takeoil level .for 'the v:aqueous .'isopropanol. distillation the TAquantity of water introducedvis suon that the concentration inthe .liquid at any pointin the :column belowv the point offwater introduction is .1in the range of from about 90 to '991mol .per ecrit, preferably 95 mol :per cent. 'The :aqueous ethanol .solution obtained .from the b'ase of 'this column 'is recycled to supply la portion 'ofthe dilution'water for the column initially described in the process of our invention. Bo'ttom 'temperatures .may range'rom 190 tota" C'.

(corrected to atmospheric pressure) butfare generally irefera-bly held toabout '97 C., `wvl-rile the top tower temperature fis .about 8056" CL corresponding to the Vboiling point of the isopropa-nolwater azeotro'pe. .Heat .input is preferably inthe .rangexof 31:.00-,150 iB. t. ol better-ns.

one .embodiment ofour invention is shown-.diagrammatically by the accompanying drawing. Referring .to the drawing, 'a `charging stock comprising essentially an aqueous solution of butyrthese `conditions ethanol is selectively washed In this downv the.` column andywithdrawn..y therefrom through line 8 after which this solution is introduced into column lll whereaoonstantboiling mixtureof ethanoland water iswithdrawn ovenhead through line l2, part ofJ iivhich` isV returned to the-top of the columnthroughline-lLas reflux. The bottoms, whichconsistsessentially. ofwater, isv :withdrawn through line I6 and* .a portion thereof transferred through. line vI8 tothe-top of column! to be recycledlas dilution water. The .remaining bottoms water .iswithdrawn through 1ine-.|1 andrun to the sewer. The overhead fracv tion from `column 4 which contains `butyraldehyde, ethyl acetate,.methyl ethyl ketone,-gmethyll propylnketone, isopropanol, water.,` and amelatively small amount (usually from .about l lio-'10 weight percent, based on the concentration of ethanol'in the original feed) of ethanoliswithdraw-n through line 20 and introduced into col-. umn 22 where the feed is extractively distilled. The vapors rising in column 22` encounter a stream of water vintroduced at. the top thereof through line 2]. .In this column butyraldehyde, ethyl acetate, and water are removed in the form "of -azeotropes as y'an overhead .fraction through 1 line 26 and partially recycled` as reflux through line 2'8. The'bottoms portion, which consists of .an aqueous solution` rof methyl ethyl ketone,

lmethyl :propyl ketone, isopropanol, and-ethanol.

is'withdrawn through line 30 and introduced finto 4'column A32 where --extractive :distillationis again effected by introducing` water-into the column through. line .35, vresulting .in methyl ethylketone, methyl propyl ketone, and azeotropic waterga- .ing overhead through vline `34, someof which. is returned `as reflux through .-line 35, whilea side stream Iof isopropanol, ethanol, land water is withdrawn through line 38l and introduced. .into column. 40. The bottomsfrom column 32, `oon-- sisting essentially of water, .is Withdrawn through line 33 and in part recycled .as dilutionl water'to 4column 22 through .line 24 while the remainder yis withdrawn through line 5-I andrun to the sewer. Isopropanolis separated .from ethanol in column 40 by means of. still ,anotherextractive distillation with water which is introduced through line 42. In 4this instance an Vazeotrope vof isopropanol and water is withdrawn through line 44V-, part of whichis .returned to column 40 throughline 46 as reflux, while a .dilute .solution of ethanol is withdrawn as .a bottom stream through line 48 and recycled through line 50 to column 4, where'it is employed as a ysource o dilutionV water.

In the above-mentioned drawing reference -to certain equipment such as pumps, reboilers, gages 'and the like which obviously would be necessary 'to operate the process lhas beenfintentionally omitted. Only sufficient equipment has :been dia.- grammatically vshown to illustrate the process, and it is intended that no undue: .limitation .rbe read into our invention by reference to'the drawing .and description thereof.

In every instance where .separation is effected by :means of extractive distillation, the amount of yheat which maybe admitted to the column employed is primarily ,determi-ned by the. .feed composition, the amount 'of-dilution Water added, and Athe type of .separation desired... In contrast -toconventional .fractionating columns, however, the .input must V.be `establishec'l between xdell .nite .maximum and minimum v'limits as. hereinbefore defined, successful operation is to beob- .tained- While our'prooess may be carried `out .atreducedyor superatmospheric pressures, lwe

` prefer-in general,v to employ atmospheric prestheseve'ral constituents Which not only boil very close together but form numerous azeotropes. This fact appears to be all the more surprising when itis realizedthat the concentration of water employed in such extractive distillation processes is generally within the relatively narrow range of 85-95 mol percent. For example, in the first extractive distillation operation only ethanol is removed from the base of the column whileall other constituents, including those which in the anhydrous state boil as much as '25 C. higher than ethanol, are removed overhead. Even under the conditions specified for this column, the separation of isopropanol from ethanolis very diflicult, and we have found it necessary to withdrawsome of the ethanol in the distillate in order to -eifect' substantially complete removal of'isopropanol. By changing conditions slightly in the second extractive distillation, the alcohols and ketones are separated from the aldehyde and ester with which they form close boiling azeotropes. In the third extractive distillation, both alcohols are separated from both ketones by taking o'f the latter as an overhead stream, in spite of the fact that the heavy ketone boils considerably higher than either of the alcohols, and that numerous azeotropes are possible. In Ythe fourth extractive distillation, by employing high dilution and precise temperature control, it is possible to achieve a sharp separation between the two most diilicultly separable constituents, namely isopropanol and ethanol; Thus, it is our observation that the components of the mixtures involved show varying degrees of non-ideality in the vpresence of water and by careful control of such variables as heat input, water concentration, and temperature gradient it is possible to effect the separations herein described.

It will be apparent, in view of the foregoin description, that the process of our invention may be modified in numerous ways without materially departing from thescope thereof. vThus, while the application of ourinvention has beendescribed principally in connection with the separation of components present in the proportions typical of those found in the water soluble chemicals stream obtained in the hydrocarbon synthesis process, it is to be strictly understood that our invention is equally applicable to the treatment of mixtures in which the common components of the aforesaid Water soluble chemicals stream are to be found in proportions substantially' dierent.

column-is from about 95 to about 99 mol perv cent, an'dwithdrawing a bottom stream containl:ing methyl ethyl ketone and an overhead fraction comprising butyraldehyde vand ethyl acetate. v- Y' 2v. In a process for-effecting separation of' butyraldehyde and ethyl acetate from aqueous mixtures Yconsisting ofv methyl ethyl ketone, butyraldehyde and ethyl acetate, the steps which comprise subjecting said mixture to fractional distillation ina column in which a heat input of from about 'to 120 B. t. u./lb. of bottoms is employed, introducing water into said column countercurently to the ow of the vaporized mixture in'an amount such that the concentration of water in the liquid at any point in the column is from about to about 99 mol per cent. and withdrawingv an aqueous bottom stream of methyl ethyl ketone and an overhead fraction of butyraldehyde and ethyl acetate.

3. Ina process for the separation of butyraldehyde and ethyl acetate from an aqueous mixture consisting of methyl ethyl ketone and said butyraldehyde and ethyl acetate, the steps which comprise subjecting said mixture to fractional distillation in a column in which a heat input of from 80 to 120 B. t. u./lb. of bottoms is employed to give a bottom tower temperature of from 82 to 94 C. and an overhead temperature of from about 68 to about 77 C., introducing water into said column in an amount such that the concentration of water in the column is from about 90 to about 99 mol per cent,-and withdrawing an overhead stream; of butyraldehyde, water. and ethyl acetate anda bottoms stream of methyl ethylketone and water;

4. In a process for separating butyraldehyde and ethyl acetate from'aqueous mixturesv containing methyl ethyl ketone and methyl propyl ketone, the steps which comprise subjecting 'said mixture to fractional distillation in a column in which a heat 'input of from 80 to 120 B. t. ku./lb. of bottoms is employed to give a bottom tower temperature of from 82 to 94 C., and an overhead temperature of from about 68 to about 77 C., introducing .water into said columnin an amountsuch that the concentration of water in the column is from about to about 99 mol per cent; and withdrawing anoverhead stream of butyraldehyde, water.. and ethyl acetate and a bottom stream containing vmethyl ethyl ketone, methyl propyl ketone, and Water.

5. The process of claim 1 in which the mixture subjected to fractional. distillation contains butyraldehyde, ethyl acetate, methyl ethyl ketone, methyl propyl ketone, isopropanol ,and

ethanol. s

5. The process of claim 3'in which themixture subjected to fractional Adistillation consists of methyl ethyl ketone,butyraldehyde, ethyl acetate, isopropanol and ethanol. l

I 7. The process of claim 4 in which the aqueous mixture subjectedv to fractional distillation contalns butyraldehyde, ethyl acetate, methyl ethyl ketone, methyl propyl ketone, isopropanol and ethanol. r

- THEODORE' Q. ELIOT.

CLIFTON S. GODDIN, JR. JOSEPH C. WEAVER, J R.

.REFERENCES CITED VI'JNITED STATES PATENTS Number Name Date 887,793 "Guillaume Mayj19, 1908 (Other references on following page) Number FOREIGN PATENTS Country Date Great Britain Feb. 17, 1948 OTHER REFERENCES Young, Distillation Principles and Processes, published 1922 by Macmillan and C'o., Ltd., London, England. (Copy in Division 6, pages 287 (last paragraph) 288 and 289.)

Mariller, Distllation et Rectification, piublislied 1925, by Donond, 92 Rue Bonaparte (VI), Paris, France. (last paragraph) 107, 412-433.)

Number (Copy in Division 25, pages 101 

1. IN A PROCESS FOR THE SEPARATION OF BUTYRALDEHYDE AND ETHYL ACETATE FROM AN AQUEOUS MIXTURE CONTAINING METHYL ETHYL KETONE, THE STEPS WHICH COMPRISE SUBJECTING SAID MIXTURE TO FRACTIONAL DISTILLATION IN A COLUMN IN WHICH A HEAT INPUT OF FROM 80 TO 120B. T. U./LB. OF BOTTOMS IS EMPLOYED INTRODUCING WATER INTO SAID COLUMN COUNTERCURRENTLY TO THE FLOW OF THE VAPORIZED MIXTURE IN AN AMOUNT SUCH THAT THE CONCENTRATION OF WATER IN THE LIQUID AT ANY POINT IN THE COLUMN IS FROM ABOUT 95 TO ABOUT 99 MOL PER CENT, AND WITHDRAWING A BOTTOM STREAM CONTAINING METHYL ETHYL KETONE AND AN OVERHEAD FRACTION COMPRISING BUTYRALDEHYDE AND ETHYL ACETATE. 